Spectkophotometric determination of the dissociation constants of n,n'-bis(3-hydroxypropyl)dithiooxamide and n,n'-bis(2-hydroxypropyl)dithiooxamide

The dissociation constants of N,N'-bis(3-hydroxypropyl)dithiooxamide and N,N'-bis(2-hydroxypropyl)dithiooxamide were determined by a spectrophotometric method using a weighted least squares technique for the calculations. For N,N'-bis(3-hydroxypropyl) dithiooxamide a thermodynamic constant pK₁^T of 11.37 was found. At ionic strength μ = 1, pK₁ = 11.27 and pK₂ = 14.29. For N,N'-bis-(2-hydroxypropyl) dithiooxamide, these values were respectively: pK₁^T = 11.11; pK₁ = 10.99 and pK₂ = 13.75.     

Studies on 1,2-Bis(O-Aminophenoxy)Ethane-N,N,N′,N′;-Tetraacetic Acid Chelates of the Tripositive Lanthanide Ions

The acid dissociation constants of 1,2-bis(cis-aminophenoxy)ethane-N,N,N′,N′;-tetraacetic acid (H₄BAPAT or H₄Z), and the stability constants of its chelates with tripositive rare-earth metal ions have been determined by the potentiometric titration and mercury indicator electrode methods at 15°, 25′ and 35°C and an ionic strength of 0.1 (KNO₃). The existence of a monohydrogen chelate species, LnHZ, and the normal chelate, LnZ^?, is illustrated. Enthalpy and entropy changes characterizing the formation of the normal chelates and the dissociation of the last two protons of chelating acid have been calculated at 25°C. These functions have been compared with corresponding values for related chelating agents.     

Amidines-XVIII: Tautomeric equilibria and pka values of N,N'-disubstituted amidines. Substituent effects

The influence of substitution of amidine group on tautomeric equilibria constants and basicities is discussed. Equations based on correlation analysis methods are derived enabling predictions of both, microscopic pK_a, values of individual tautomers, measured macroscopic pK_a values of the tautomeric mixture, as well as the tautomeric equilibrium constant (as pK_T). It is shown that pK_arn values of unsymmetrically N,N'-disubstituted amidines should obey a non-linear relation with σ° constants, and only for symmetrically N,N'-disubstituted amidines obey the linear Hammett equation. Tautomeric equilibrium constants of N,N'-disubstituted amidines correlate withσ° substituent constants. The methods of prediction of pK_a value of both tautomers and pK_T value are proposed.Derived relations are applied to the series of N,N'-diphenylacetamidines and benzamidines.     

3,3'-Dihydroxybenzidine-n,n,n',n'-tetraacetic acid as a metallofluorescent indicator in edta titrations

3,3'-Dihydroxybenzidine-N,N,N',N'-tetraacetic acid has been prepared and examined as a metallofluorescent indicator in compleximetric titrations. Copper(II) and lead(II) are determined by titration with EDTA in the presence of the indicator, the blue fluorescence of which is restored at the end-point. Manganese, zinc, cobalt and cadmium can also be determined if a dyestuff such as Rhodamine B is present along with the indicator.     

Spectrophotometric determination of the dissociation constants of n.n'-bis(2-hydroxyethyl)dithio-oxamide

The dissociation constants of N, N'-bis(2-hydroxyethyl)dithio-oxamide were determined by a spectrophotometric method. The dissociation constants were calculated by means of a weighted least squares technique. N, N'-Bis(2-hydroxyethyl)dithio-oxamide was found to be a dibasic acid with a thermodynamic dissociation constant pK1-11/04. At ionic strength μ - 0.5, pK1 - 10.71 and pK2 13.92.     

The titrimetric determination of beryllium(II) with 1,2-phenylenediamine-N,N,N′,N′-tetraacetic acid

Beryllium (ca. 10^?2?10^?4 M) is determined by adding excess of 1,2-phenylenediamine-N,N,N′, N′-tetraacetic acid (PhDTA, H₄L) and back-titrating with copper(II); arsenazo-I serves as indicator. Formation constants of BeL and BeHL were determined by potentiometry: log K_BeL=6.48±0.02 and log K^H_BeHL=3.48±0.03 (25°C, I=1 M in NaClO₄). Expressions for the titration curve are given together with theoretical errors.     

Spectrophophotometric determination of manganese with n,n,n',n'-tetrakis(2-hydraxypropyl)ethylenediamine

A new spectrophotometric method for the determination of manganese with N,N,N,N'-tetrakis-(2-hydroxypropyl) ethylenediamine has been developed. The sensitivity is 0.12 μm of Mn per cm² for log I₀/I= 0.001 and Beer's law is obeyed between 2 and 100 p.p.m. of manganese. An ionexchange separation of interfering ions was satisfactory for thc analysis of a variety of National Bureau of Standards samples with good accuracy. The standard deviation with a Mn-bronze was 1.25%.     

Some metallofluorescent derivatives of 2,2'-diamino-diphenyl-n,n,n',n'-tetraacetic acid

The N,N,N',N'-tetraacetic acid derivatives of five 4,4'-disubstituted 2,2'-diaminodiphenyls have been prepared and their fluorescent properties examined. 2,2'-Diaminodiphenyl-4,4'-dicarboxylic acid-N,N,N',N'-tetraacetic acid exhibits intense fluorescence in aqueous solution above pH 4, and forms stable non-fluorescent l:1 complexes with copper(II) and nickel(II) ions at pH 7.5. The quenching of the fluorescence of the compound by nickel(II) may be used in the fluorimetric determination of nickel.     

The Stabilities and Thermodynamic Properties of Manganese(II) and Nickel(II) Chelates of Trans-1,2-Diaminocyclohexane-N,N, N', N'-Tetraacetic Acid

The interaction between trans-1,2-diaminocyclohexane-N, N, N', N'-tetraacetic acid (H₁DCTA or H₄Z) and Mn(II) and Ni(II) ions has been investigated. The formation constants of the hydrogen chelates (MHZ^?), and of the normal chelates (MZ^2?), have been measured at 20, 30 and 40°C, and an ionic strength of 0.10 (KNO₃). The former was done by a titration technique and the latter by a mercury indicator electrode method. Enthalpy and entropy changes characterizing the formation of the normal chelates have been calculated at 25°C.     

Microwave spectra of isotopic glycolaldehydes,substitution structure,intramolecular hydrogen bond and dipole moment

The microwave spectra of ¹³CH₂OH-CHO, CH₂OH-¹³CHO, and CH₂OH-CH¹⁸O are reported and have been used in combination with previously published data on other monosubstituted glycolaldehydes to determine the substitution structure of the molecule as r(CO) = 1.209 Å, r(C-O) = 1.437 Å, r(C-C) = 1.499 Å, r(O-H) = 1.051 Å, r(C-H_ald) = 1.102 Å, r(C-H_alc) = 1.093 Å, r(O β H) = 2.007 Å, r(O β O) = 2.697 Å, ∠(C-CO) = 122°44', ∠(C-C-H_ald) = 115°16', ∠(C-C-O) = 111°28', ∠(C-O-H) = 101°34', ∠(C-C-H_alc) = 109°13', ∠(H-C-H) = 107°34', ∠(O-H β O) = 120°33', ∠(H β OC) = 83°41', and ∠(O-H, C0) = 24°14'. The intramolecular hydrogen bond and the other structural parameters are discussed and compared to related molecules. The dipole moment is redetermined to be μ_a = 0.262 ±0.002 D, μ_b = 2.33 ± 0.01 D, and μ_tot = 2.34 ± 0.01 D. Relative intensity measurements yielded 195 ± 30 cm^?1 for the C-C torsional fundamental and 260±40 cm^?1 for the lowest in-plane skeletal bending mode. Computations performed by the CNDO/2 method correctly predict the observed cis hydrogen-bonded conformer to be the energetically favoured one and in addition yield some indication of the existence of at least two other non-hydrogen-bonded forms of higher energy.     

Spectrophotometric or absorptiometric determination of copper with 2,2'-diaminodiethylether-n,n.n', n'-tetraacetic acid

A spectrophotometric determination of copper with 2,2'-diaminodiethylether-N,N,N',N'-tetraacetic acid is proposed. Maximum absorbance is obtained at 720 mμ at pH 2 (1–3) and 25–650 μg Cu/ml can be determined. The reaction is unaffected by temperature or time of standing, and very few ions interfere. A 1 : 1 copper-EEDTA complex is formed.     

Alkoxycarbonyl-isocyanate durch thermolytische spaltung von n-alkoxycarbonyl-substituierten schwefelimiden

N,N'-Bis(alkoxycarbonyl)sulfurdiimides S(N-CO-OR)₂ and N-Sulfinyl-carbamates RO-CO-NSO (R=alkyl) can be transformed into alkoxycarbonyl-isocyanates and several by-products by thermolytical cleavage at 180–210°. The identification of the by-products and their possible formation are described.     

Interaction of calf thymus DNA with N,N′-Bis(3,4-dihydroxybenzylidene)-1,2-diaminobenzene ligands

In the present study, at first, N,N′-bis(3,4-dihydroxyhenzylidene)-1,2-diaminobenzene (BDBDAB), has been synthesized by combination of 1,2-diaminobenzene and 3,4-dihydroxybenzaldehyde in a solvent system. These ligand containing ortho-quinone functional groups were characterized using UV-VIS and IR spectroscopies. Subsequently, the interaction between native calf thymus deoxyribonucleic acid (ct-DNA) and BDBDAB was investigated in 10 mM Tris-HCl buffer solution, pH 7.2, using UV-visible absorption and fluorescence spectroscopies, thermal denaturation technique, viscosity measurement, and cyclic voltametry. From spectrophotometric titration experiments, the binding constants of BDBDAB with double stranded DNA were found to be (0.9 ± 0.1) × 10⁴ M⁻¹. The magnitude of the interaction between the ligands and DNA can be quantified by using the Stern-Volmer equation. From the plot of I ₀/I versus [DNA]/[BDBDAB] the quenching constants (K _SV) were obtained and found to be 5.6 ± 0.2. Thermal denaturation experiments represent the increasing of melting temperature of DNA (about 3.2°C) due to binding of BDBDAB. There is no increasing of viscosity was observed in addition of BDBDAB to DNA. The electroactivity of the quinone moiety in N,N′-bis(3,4-dihydroxybenzylidene)-1,2-diaminobenzene bound to DNA could be employed as cyclic voltametry to obtain binding constant. These results suggest that interaction with the grooves could be the principal mode of binding of BDBDAB to double stranded ct-DNA.     

Spectrophotometric study of n,n'-bis(m-sulphobenzyl)dithio-oxamide as a reagent for nickel(II)

N,N'-Bis(m-sulphobenzyl) dithiooxamide forms a water-soluble intensely red chelate with nickel-(II) in buffered solutions at pH 10, A 1 Ni : 1R complex is obtained. The absorption maximum of the complex lies at 500 mμ, where the absorbance of (SB)₂DTO is negligible. The molar extinction coefficient is ca, 6962. Beer's law is obeyed over the range from 0.5 μg to 50 μg per ml.     

Solvent effects on the dissociation of aliphatic carboxylic acids in water—N,N-dimethylformamide mixtures

The autoprotolysis constants of several water-_N,N-dimethylformamide mixtures were determined. The acid dissociation constants of formic, acetic, propionic, n-butyric, isobutyric, n-valeric, isovaleric, 2-methylbutyric and trimethylacetic acids were evaluated in the same media by potentiometric titration. Empirical equations for the calculation of autoprotolysis constants and acid dissociation constants at 25° C in the mixed solvents are proposed. Approximate solvation numbers were obtained by multiple linear regression analyses of pK_a values.     

Synthesis,spectral, catalytic,and thermal studies of vanadium complexes with quadridentate schiff bases

The paper reports the synthesis and characterization of vanadium complexes of N,N′-(±)-trans-bis(2,4-dihydroxyacetophenone)-1,2-cyclohexanediamine (H₂L¹) and N,N′-(±)-trans-bis(2,4-dihyroxy-5-nitroacetophenone)-1,2-chyclohexanediamine (H₂L²). All the complexes were characterized by elemental analysis, magnetic susceptibility measurements, infrared and electronic spectra, and thermogravimetric analysis. The X-ray patterns of the [VO(L¹)] · H₂O (I) and [VO(L²)] · H₂O (II) complexes show the monoclinic system with the unit cell parameters a = 26.1352, b = 11.7149, c = 6.0401 β = 115.38° and a = 29.3787, b = 12.9398, c = 5.9175 β = 96.84°, respectively. The complexes I and II catalyze the oxidation of styrene in the presence of hydrogen peroxide.     

Thermodynamics and kinetics of complexation of iron(III) ion by picolinic and dipicolinic acids

The complexation reactions of iron(III) with 2-pyridine carboxylic acia (picolinic acid) and 2,6-pyridine dicarboxylic acid (dipicolinic acid) in aqueous solutions have been studied by spectrophotometric and stopped flow techniques. Equilibrium constants were determined for the 1 : 1 complexes at temperatures between 25 and 80°C. The values obtained are: Picolinic Acid (HL): Fe³⁺+ H₂L⁺? FeHL³⁺+H+(K₁ = 2.8,ΔH = 2 kcal mole^?1 at 25°C, μ = 2.67 M) Dipicolinic Acid (H₂D): Fe³⁺+H₂D? FeD⁺+2H⁺(K₁K_1A= 227 M, ΔH = 3.4 kcal mole^?1 at 25°C,μ = 1.0 M). The rate constants for the formation of these complexes are also given. The results are used to evaluate the effects of these two acids upon the rate of dissolution of iron(III) from its oxides.     

Mischligandenkomplexe einiger Seltener Erden

Biligand complexes of the 1∶1Ln(III)-1,2-diaminocyclo-hexane-tetraacetic acid (CDTA) chelate with hydroxy acids [where hydroxy acids = salicylic acid (SA); Sulphosalicylic acid (SSA) and 8-hydroxyquinoline-5-sulphonic acid (HQSA)] have been investigated by potentiometric titration. Their formation constants have been calculated (μ=0.1M-KNO₃; andt=30±1°C) as 4.60±0.03, 5.46±0.03, 5.87±0.05; 3.12±0.04, 3.95±0.05, 4.42±0.07; 2.73±0.06, 3.45±0.05 and 3.90±0.08 forLn(III)-CDTA-SA,-SSA, and-HQSA respectively (whereLn=La, Pr or Nd). The value of logK _MAB follows the order: La(III)     

O-(2-Thiazolylazo)-4-Chlorophenol Complexes and Their Utility as Metallo-Chromic Indicators for Nickel(II) Ion

Abstract

The stability constants of the complexes formed between o-(2-thiazoiylazo)-4-chlorophenol (TACL) and bivalent metal ions obtained spectrophotometrically were: logK_MnR = 2.86, logK_CoR = 5.37, logK_NiR = 6.12, logK_{NiR 2} = 5.44, logK_CuR = 8.39, logK_ZnR = 4.54, logK_{ZnR 2} = 4.43 and logK_CuR = 5.65, (20°c, μ = 0.1, 10% v/v aqueous dioxane). These values coincided well with the Irving-Williams order.

The acid dissociation constants of analogous new dyestuffs synthesized in our Laboratory, o-(2-thiazolylazo)-phenol, o-(2-thiazolylazo)-4-bromophenol and o-(2-thiazoly-lazo)-4- iodophenol were 7.36, 7.35, and 7.25, respectively (20°C, μ = 0.1, 10% v/v aqueous dioxane).

TACL was found to be applicable as a metallochromic indicator for the titration of nickel(II) in weakly acidic media using EDTA as a titrant. No heating was required.     

Syntheses and structures of nine-coordinate NH4[HoIII(Edta)(H2O)3] · 1.5H2O, (NH4)4[Ho 2 III (Dtpa)2] · 9H2O, and (NH4)3[HoIII(Ttha)] · 5H2O complexes

The three title complexes, NH₄[Ho^III(Edta)(H₂O)₃] · 1.5H₂O (I) (H₄Edta = ethylenedianine-N,N,N′,N′-tetraacetic acid), (NH₄)₄[Ho ₂ ^III (Dtpa)₂] · 9H₂O (II) (H₅Dtpa = diethylenetriamine-N,N,N′,N″,N″-entaacetic acid), and (NH₄)₃[Ho^III(Ttha)] · 5H₂O (III) (H₆ Ttha = triethylenetetramine-N,N,N′,N″,N?,N?-hexaacetic acid), have been prepared and characterized by FT-IR, elemental analyses, and single-crystal X-ray diffraction technique. Complex I has a nine-coordinate mononuclear structure with distorted monocapped square antiprismatic conformation and its crystal structure belongs to orthorhombic system and Fdd2 space group. The crystal data are as follows: a = 19.343(9), b = 35.125(17), c = 12.364(6) Å, V = 8400(7) ų, Z = 16, M = 552.26, ρ_calcd = 1.747 g cm^?3 μ = 3.828 mm^?1, and F(000) = 4368. Complex II has a binuclear nine-coordinate pseudomonocapped square antiprismatic conformation and its crystal structure belongs to triclinic system and space P1 group. The crystal data are as follows: a = 9.7637(16), b = 9.9722(16), c = 12.945(2) Å, α= 85.853(2)°, β = 77. 140(2)°, γ = 77.140(2)°, V = 1198.4(3) ų, Z = 1, M = 1340.80, ρ_calcd = 1.858 g cm^?3, μ = 3.380 mm^?1, and F(000) = 674. As for complex III, it also has nine-coordinate mononuclear structure with distorted tricapped trigonal prism and its crystal structure belongs to monoclinic system andP2₁/c space group. The crystal data are as follows: a = 10.349(3), b = 12.760(4), c = 23.142(7) Å, β = 91.020(6)°, V = 3055.6(16) ų, Z = 2, M = 797.55, ρ_calcd = 1.734 g cm^?3, μ = 2.674 mm^?1, and F(000) = 1624. The results showed that although the ligands are different from one another in the shape and the numbers of coordination atoms, they all have nine-coordinate structures. However, one of them has binuclear structure and the other two have mononuclear structures because of the difference of the ligands.